CODEWITHSUNDEEP
ruser-defined-functions
user5457414
user5457414

Reputation: 137

Logical arguments in user defined functions in r

I'm trying to write a function in r that includes a named argument with three options. (What I want to do is find the area in the right tail of a normal curve, the left tail, or both tails.) Is this possible? I've come up with this, but I get an error when I try it with right=BOTH.

st.pnorm<-function(x,µ,ø,right=c('TRUE','FALSE','BOTH')){  
  if (right==FALSE) return({pnorm((x-µ)/ø)})  
  if (right==TRUE) return({1-(pnorm((x-µ)/ø))})  
  if (right==BOTH) return({x*2})  
}

st.pnorm(19.4,11,8.4,right='BOTH')
Error in st.pnorm(19.4, 11, 8.4, right = "BOTH") :
object 'BOTH' not found

(I know x*2 isn't correct, but I want to see if I can get this to work structurally before I actually write that code.)

Upvotes: 5

Views: 10819

Answers (2)

StevenHolland
StevenHolland

Reputation: 106

That your named argument has three options suggests that strings (as you've set it up) are a better way to go than Boolean values. Calling the parameter tail, instead of right, would make your intent clearer. 

st.pnorm<-function(x,µ,ø,tail=c('right','left','both')){  
  if (tail=='left') return({pnorm((x-µ)/ø)})  
  if (tail=='right') return({1-(pnorm((x-µ)/ø))})  
  if (tail=='both') return({x*2})  
}

Upvotes: 1

amwill04
amwill04

Reputation: 1360

st.pnorm<-function(x,µ,ø,right=TRUE){  
     if (right==FALSE) return({pnorm((x-µ)/ø)})  
     if (right==TRUE) return({1-(pnorm((x-µ)/ø))})  
     if (right=="BOTH") return({x*2})  
 }

TRUE and FALSE should be enclosed in quotes while BOTH does need to be, hence if (right=="BOTH"). Also with right=TRUE you are declaring a default value to the TRUE.

EDIT

As @KonradRudolph points out in the comments, the if statement is checking if, what is inside the brackets, is TRUE or not. If it is TRUE then it will action otherwise it will skip. Therefore as right takes on TRUE or FALSE the above could be re written as the following:

st.pnorm<-function(x,µ,ø,right=TRUE){  
     if (!right) return({pnorm((x-µ)/ø)})  
     if (right) return({1-(pnorm((x-µ)/ø))})  
     if (right=="BOTH") return({x*2})  
 }

Where ! acts as the not operator.

Upvotes: 4

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